1. Field of the Invention
The present invention is generally directed to telecommunication networks. In particular, the present invention is directed to methods for re-routing data packets on a data switching network.
2. Discussion of the Related Art
In a packet-switching network, such as for example the Internet, which is usually composed of a plurality of sub-networks, data packets from a source node are potentially transmitted to a destination node via a plurality of intermediate and/or access nodes of the individual sub-networks. In addition to containing information, the data packets particularly contain a destination address. The intermediate and/or access nodes contain what is referred to as a routing table for determining a traffic path in which each destination address of a data packet has a destination address of that node such as an intermediate node or an access node, to which the data packet is forwarded allocated to it. Thus, when a data packet arrives at such a node, the data packet is forwarded to the node corresponding to its destination address entry in the routing table.
The data transmission in such a packet-switching network is normally connectionless, i.e. the data packets with identical source and destination address are transported independently of one another, so that neither the sequence nor a delivery of the data packets at the destination node is guaranteed, such as under OSI Layer 3 Protocol. However, a quality of the transmission of data packets between source and destination node such as certain bandwidth, delay times and a specific throughput, can not be promised.
Video transmission services, such as video on demand and various telephone services, such as voice over IP in the Internet, require a dependable and fast data transmission with an assured quality.
An “Internet Draft” document authored by K. Nichols and S. Blake that was published by the Internet Engineering Task Force in February 1998 (Internet site: http://www.ietf.org/internet-drafts/draft-nichols-dsopdef-00.txt) proposes a method that enables an accelerated transmission of data packets from a source node to a destination node.
For data packets to be forwarded especially fast, specific bits of what is referred to as the TOS (type of service) byte in the header part of such a data packet are set. Such data packets can be divided into various classes on the basis of the bits that are set in the TOS byte. According to their class, the data packets identified with the set bits are given privileged handling in the intermediate nodes via which such data packets are transmitted from the source node to the destination node, as a result an accelerated forwarding to the next node, intermediate or destination node is achieved.
A critical disadvantage of this method is that the privileged handling in the forwarding of the data packets identified with the set bits leads to considerable delays in the forwarding of the data packets to be transmitted normally.
Moreover, it is not only the destination addresses but also the respective TOS bytes that must be taken into consideration in every intermediate node when forwarding the data packets.
Another “Internet Draft” document authored by Y. Bernet, R. Yavatkar, P. Ford, F. Baker and L. Zhang that was published by the Internet Engineering Task Force in March 1998 (Internet site: http://ietf.org/internet-drafts/draft-bernet-intdiff-00.txt) presents a method that, with the assistance of the above-explained method, combines a plurality of demands made of the Internet for a guaranteed quality for the transmission of data packets into classes. A corresponding quality for the transmission of data packets is assured according to such a class.
Since a required quality for the transmission of data packets with a privileged handling thereof on the basis of the aforementioned, set bits in the TOS byte is assured, this method can be reduced to the initially explained approach. However, this method too suffers from the disadvantages mentioned above.
Another approach to offering the user of a video transmission service of a bandwidth suitable for the transmission of data packets is disclosed by U.S. Pat. No. 5,732,078.
That patent discloses an arrangement of an access node to the Internet that assures a bandwidth requested by the user for the transmission of data packets by re-routing data packets onto an alternate network. The re-routing of the data packets requires a user to request a specific bandwidth for the transmission of data packets from his user terminal device to a destination node. Then, the access node to which the user terminal device is connected sets up a point-to-point connection to the access node to which the destination node is connected via the alternate network offering the requested bandwidth.
To re-route the data packets for whose transmission the user requests an assured bandwidth onto the alternate network, an existing routing table in the access node to which the user terminal device is connected is finally modified such that, in addition to containing the respective destination addresses of the nodes to which data packets are respectively forwarded, it also contains the source addresses of the data packets to be re-routed due to a quality requested by the user. According to a modification of the method presented in the U.S. Pat. No. 5,732,078 mentioned above, a connection-individual or a transmission-individual particular, also know as an application port number, is entered into the routing table.
On the basis of the additionally stored source address and the connection-Individual or transmission-individual particular in the routing table, the data packets arriving at such an access node can be selected according to whether they are routed over the ordinary Internet or via the alternate network.
This method is very involved since a separate connection via the alternate network must be set up for every transmission of data packets with a requested bandwidth that is initiated by a user.
Additionally, the routing table must be modified in every access node to which user terminal devices are connected, namely after every transmission of data packets with a specific bandwidth initiated by a user.
Also to be considered is that all data packets arriving at such an access node are examined for their source address in order for the connection-individual or transmission-individual particular, with reference to the source address, to be re-routing onto the alternate network.
In their Master Thesis, “Support Qos in IP over ATM”, June 1997 (1997–06), National Taiwan University of Science and Technology, Taipei, Taiwan, (available online), Gung-Chou Lai and Ruay-Shiung Chang state that it is possible in a switching system to use the field TOS (Type of Service) in the header part of data packets which are to be switched or transmitted to determine whether an existing Virtual Channel is used or a new Virtual Channel has to be initiated.